Memory provides data storage for electronic systems. Flash memory is one type of memory, and has numerous uses in computers and other devices. For instance, personal computers may have BIOS stored on a flash memory chip. As another example, flash memory is used in solid state drives to replace spinning hard drives. As yet another example, flash memory is used in wireless electronic devices as it enables manufacturers to support new communication protocols as they become standardized, and to provide the ability to remotely upgrade the devices for improved or enhanced features.
A typical flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. The flash memory may be erased and reprogrammed in blocks. NAND may be a basic architecture of flash memory. A NAND cell unit comprises at least one selecting device coupled in series to a serial combination of memory cells (with the serial combination commonly being referred to as a NAND string). Example NAND architecture is described in U.S. Pat. No. 7,898,850.
Memory cell strings in flash or other memory may be arranged to extend horizontally or vertically. Vertical memory cell strings reduce horizontal area of a substrate occupied by the memory cells in comparison to horizontally extending memory cell strings, albeit typically at the expense of increased vertical thickness.
Formation of vertically-extending strings of memory cells commonly includes etching of individual channel openings through multiple alternating tiers of material. Multiple materials are then deposited into the channel openings, with the channel material being one of the latter materials so-deposited. The channel material ideally electrically couples with conductive or semiconductive material there-below. Accordingly, the respective materials first-deposited in the channel opening need to be removed from being centrally over the base of the channel opening such that the channel material when it is deposited may make electrical connection with the material at the base of the channel openings. These earlier materials are typically so-removed by exposure to wet isotropic HF and/or H3PO4 etching. These earlier materials can be difficult to remove from the base of the channel openings. This is particularly so where a silicon nitride-comprising region atop the alternating materials through which the channel openings are formed has less opening width at its elevationally-outermost surface than at its elevationally-innermost surface.